The Unprecedented Tetrakis-(disulfato)-silicate Anion [Si(S_2O_7)_4]~(4-), its Germanium Congener [Ge(S_2O_7)_4]~(4-), and the Tris-(disulfato)-metallates [M(S_2O_7)_3]~(2-) (M = Si, Ge, Ti), Stabilized by Divalent Counter Cations B~(2+) (B = Sr, Ba, Pb)

摘要

The reaction of oleum (65% SO_3) with the tetrachlorides of silicon, germanium, and titanium, respectively, led to the complex disulfates Sr_2[M-(S_2O_7)_4] (M=Si, Ge), Ba[M(S_2O_7)_3] (M=Si, Ge, Ti) and Pb[M(S_2O_7)_3] (M=Ge, Ti) if strontium, barium, and lead were used as divalent counter cations. The strontium compounds exhibit the unique tetrakis-(disulfato)-metallate anions [M(S_2O_7)_4]~(4-) with the silicon and germanium atoms in octahedral coordination of two chelating and two monodentate disulfate groups. All of the other compounds display tris-(disulfato)-metallate anions [M(S_2O_7)_3]~(2-) with three chelating disulfate groups surrounding the M atoms. Thermoanalytical investigations on the germanium compounds Sr_2[Ge(S_2O_7)_4] and Ba[Ge-(S_2O_7)_3] revealed their decomposition in multi-step processes leading to a mixture of BSO_4 and BGe_4O_9 (B = Sr, Ba), while the thermal degradation of Pb[Ti(S_2O_7)_3] yields PbTiO_3. For selected examples, IR data are additionally presented.